Unless you've developed an eye for the fluid color or nose for burned fluid, you have a couple options open to you. One is to simply change out the fluid, then you can put the transmissions fluid change schedule back on track, A lot of used car buyers do that to all the fluids and filters after purchase so they have a baseline for future maintenance.

Another option is to send a sample of fluid out for a used oil analysis. You didn't mention which model you drive. Sampling the fluid may make best sense if you're using the $14.50/qt transmission fluid. It gets expensive to willy-nilly change that expensive fluid more often than needed, though it's still cheaper than transmission repair. For older transmissions, the price for 7 to 8 quarts needed for changeout is practically negligible.

__________________
95 E320 Cabriolet, 169K

Change the fluid, also do the rear end fluid at the same time. That way you can do it every other or 3rd trans fluid change. Fugure 30k for the trans 60k-90k for the rear gear lube.

__________________
2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200